Trypanosoma congolense is an important African cattle parasite indirectly responsible for much protein malnutrition in man. We are studying antigenic variation in this trypanosome. Stabilates from the first and second post-Glossinia blood stream variants of a cloned T. congolense strain will be prepared and the parasites propagated in irradiated rats. Blood stream variant (BSV) coat proteins 1 and 2 will be isolated by the Lentil-Lectin column method and their structure partially characterized by amino acid analysis and peptide mapping of I-125 labeled derivatives and automated amino acid sequence analysis. Antibodies to BSV coat proteins will be produced. The BSV-1 and 2-trypanosomes will be adapted to culture and we will attempt to induce antigenic variation in culture with antibodies. We will see if successive gene induction or a post-transcriptional control mechanism can account for antigenic variation. We will look for phenotypic gene expression, i.e. the presence of small quantities of post BSV-1 coat protein in BSV-1 trypanosomes, using the highly sensitive microliter plate radioimmuno assay and phage inactivation techniques. The simultaneous presence of more than one BSV mRNA will be tested and we will assess the activity of the gene for the BSV-2 coat protein in BSV-1 trypanosomes.